Localization of somatostatin-, substance P- and calcitonin-like immunoreactivity in the neural ganglion of Ciona intestinalis L. (Ascidiaceae)

Neuropeptides and receptors in the cephalochordate: A crucial model for understanding the origin and evolution of vertebrate neuropeptide systems

Genomes and transcriptomes from diverse organisms are providing a wealth of data to explore the evolution and origin of neuropeptides and their receptors in metazoans. While most neuropeptide-receptor systems have been extensively studied in vertebrates, there is still a considerable lack of understanding regarding their functions in invertebrates, an extraordinarily diverse group that account for the majority of animal species on Earth. Cephalochordates, commonly known as amphioxus or lancelets, serve as the evolutionary proxy of the chordate ancestor. Their key evolutionary position, bridging the invertebrate to vertebrate transition, has been explored to uncover the origin, evolution, and function of vertebrate neuropeptide systems. Amphioxus genomes exhibit a high degree of sequence and structural conservation with vertebrates, and sequence and functional homologues of several vertebrate neuropeptide families are present in cephalochordates. This review aims to provide a comprehensively overview of the recent findings on neuropeptides and their receptors in cephalochordates, highlighting their significance as a model for understanding the complex evolution of neuropeptide signaling in vertebrates.

Characterization of an evolutionarily conserved calcitonin signaling system in a lophotrochozoan, the Pacific oyster (Crassostrea gigas)

In Protostoma, the diuretic hormone 31 (DH31) signaling system was long considered as the orthologue of the chordate calcitonin (CT) signaling system. Using the Pacific oyster (Crassostrea gigas) transcriptomic database GigaTON (http://ngspipelines-sigenae.toulouse.inra.fr/), we characterized seven G-protein-coupled receptors (GPCRs) named Cragi-CTR1/7 and phylogenetically related to chordate CT receptors (CTRs) and to protostome DH31 receptors. Two CT Precursors (Cragi-CTP1 and Cragi-CTP2) containing two CT-type peptides and encoded by two distinct genes with a similar organization were also characterized. These oyster neuropeptides (Cragi-CT1/2) exhibit the two N-terminal paired cysteine residues and except CTP2 derived peptide (Cragi-CTP2dp) the C-terminal proline-amide motif typical of deuterostome CT-type peptides. All mature Cragi-CTs but Cragi-CTP2dp were detected in visceral ganglion (VG) extracts using mass spectrometry. Cell-based assays revealed that the formerly characterized oyster receptors Cg-CTR and Cragi-CTR2 were specifically activated by Cragi-CT1b and Cragi-CT2, respectively. This activation does not require the co-expression of receptor activity-modifying proteins (RAMPs). Thus, the oyster CT signaling appears functionally more closely related to the vertebrate CT/CTR signaling than to the (Calcitonin Gene Related Peptide) CGRP/CLR signaling. Gene expression profiles in different adult tissues and in oysters acclimated to brackish water suggest the potential implication of both Cg-CT-R/Cragi-CT1b and Cragi-CTR2/Cragi-CT2 in water and ionic regulations, though with apparently opposite effects. The present study represents the first comprehensive characterization of a functional CT-type signaling system in a protostome and provides evidence for its evolutionarily ancient origin and its early role in osmotic homeostasis.

Evolution of neuropeptide signalling systems

Neuropeptides are a diverse class of neuronal signalling molecules that regulate physiological processes and behaviour in animals. However, determining the relationships and evolutionary origins of the heterogeneous assemblage of neuropeptides identified in a range of phyla has presented a huge challenge for comparative physiologists. Here, we review revolutionary insights into the evolution of neuropeptide signalling that have been obtained recently through comparative analysis of genome/transcriptome sequence data and by ‘deorphanisation’ of neuropeptide receptors. The evolutionary origins of at least 30 neuropeptide signalling systems have been traced to the common ancestor of protostomes and deuterostomes. Furthermore, two rounds of genome duplication gave rise to an expanded repertoire of neuropeptide signalling systems in the vertebrate lineage, enabling neofunctionalisation and/or subfunctionalisation, but with lineage-specific gene loss and/or additional gene or genome duplications generating complex patterns in the phylogenetic distribution of paralogous neuropeptide signalling systems. We are entering a new era in neuropeptide research where it has become feasible to compare the physiological roles of orthologous and paralogous neuropeptides in a wide range of phyla. Moreover, the ambitious mission to reconstruct the evolution of neuropeptide function in the animal kingdom now represents a tangible challenge for the future.

Summary: A review of the revolutionary advances in our knowledge of the evolution of neuropeptide signalling systems that have been enabled by comparative genomics and neuropeptide receptor deorphanisation.

Neuropeptides, hormone peptides, and their receptors in Ciona intestinalis: an update

The critical phylogenetic position of ascidians leads to the presumption that neuropeptides and hormones in vertebrates are highly likely to be evolutionarily conserved in ascidians, and the cosmopolitan species Ciona intestinalis is expected to be an excellent deuterostome Invertebrate model for studies on neuropeptides and hormones. Nevertheless, molecular and functional characterization of Ciona neuropeptides and hormone peptides was restricted to a few peptides such as a cholecystokinin (CCK)/gastrin peptide, cionin, and gonadotropin-releasing hormones (GnRHs). In the past few years, mass spectrometric analyses and database searches have detected Ciona orthologs or prototypes of vertebrate peptides and their receptors, including tachykinin, insulin/relaxin, calcitonin, and vasopressin. Furthermore, studies have shown that several Ciona peptides, including vasopressin and a novel GnRH-related peptide, have acquired ascidian-specific molecular forms and/or biological functions. These findings provided indisputable evidence that ascidians, unlike other invertebrates (including the traditional protostome model animals), possess neuropeptides and hormone peptides structurally and functionally related to vertebrate counterparts, and that several peptides have uniquely diverged in ascidian evolutionary lineages. Moreover, recent functional analyses of Ciona tachykinin in the ovary substantiated the novel tachykininergic protease-assoclated oocyte growth pathway, which could not have been revealed in studies on vertebrates. These findings confirm the outstanding advantages of ascidians in understanding the neuroscience, endocrinology, and evolution of vertebrate neuropeptides and hormone peptides. This article provides an overview of basic findings and reviews new knowledge on ascidian neuropeptides and hormone peptides.

Calcitonin in a protochordate, Ciona intestinalis--the prototype of the vertebrate calcitonin/calcitonin gene-related peptide superfamily

The calcitonin (CT)/CT gene-related peptides (CGRPs) constitute a large peptide family in vertebrates. However, no CT/CGRP superfamily members have so far been identified in invertebrates, and the evolutionary process leading to the diverse vertebrate CT/CGRP superfamily members remains unclear. In this study, we have identified an authentic invertebrate CT, Ci-CT, in the ascidian Ciona intestinalis, which is the phylogenetically closest invertebrate chordate to vertebrates. The amino acid sequence of Ci-CT was shown to display high similarity to those of vertebrate CTs and to share CT consensus motifs, including the N-terminal circular region and C-terminal amidated proline. Furthermore, the Ci-CT gene was found to be the only Ciona CT/CGRP superfamily gene. Ci-CT also exhibited less potent, but significant, activation of the human CT receptor, as compared with salmon CT. Physiological analysis revealed that Ci-CT reduced the osteoclastic activity that is specific to vertebrate CTs. CD analysis demonstrated that Ci-CT weakly forms an alpha-helix structure. These results provide evidence that the CT/CGRP superfamily is essentially conserved in ascidians as well as in vertebrates, and indicate that Ci-CT is a prototype of vertebrate CT/CGRP superfamily members. Moreover, expression analysis demonstrated that Ci-CT is expressed in more organs than vertebrate CTs in the cognate organs, suggesting that an original CT/CGRP superfamily member gene was also expressed in multiple organs, and each CT/CGRP superfamily member acquired its current specific tissue distribution and physiological role concomitantly with diversification of the CT/CGRP superfamily during the evolution of chordates. This is the first report on a CT/CGRP superfamily member in invertebrates.

Lateral line, otic and epibranchial placodes: developmental and evolutionary links?

Two embryonic cell populations, the neural crest and cranial ectodermal placodes, between them give rise to many of the unique characters of vertebrates. Neurogenic placode derivatives are vital for sensing both external and internal stimuli. In this speculative review, we discuss potential developmental and evolutionary relationships between two placode series that are usually considered to be entirely independent: lateral line placodes, which form the mechanosensory and electroreceptive hair cells of the anamniote lateral line system as well as their afferent neurons, and epibranchial placodes (geniculate, petrosal and nodose), which form Phox2b(+) visceral sensory neurons with input from both the external and internal environment. We illustrate their development using molecular data we recently obtained in shark embryos, and we describe their derivatives, including the possible geniculate placode origin of a mechanosensory sense organ associated with the first pharyngeal pouch/cleft (the anamniote spiracular organ/amniote paratympanic organ). We discuss how both lateral line and epibranchial placodes can be related in different ways to the otic placode (which forms the inner ear and its afferent neurons), and how both are important for protective somatic reflexes. Finally, we put forward a highly speculative proposal about the original function of the cells whose evolutionary descendants today include the derivatives of the lateral line, otic and epibranchial placodes, namely that they produced sensory receptors and neurons for Phox2b-dependent protective reflex circuits. We hope this review will stimulate both debate and a fresh look at possible developmental and evolutionary relationships between these seemingly disparate and independent placodes.

Evolution of the CT/CGRP family: comparative study with new data from models of teleosts, the eel, and cephalopod molluscs, the cuttlefish and the nautilus

In mammals, alternative splicing of the calcitonin gene generates two distinct peptides: calcitonin (CT), synthesised in the thyroid C cells and involved in the regulation of calcium metabolism, and calcitonin gene-related peptide (CGRP), brain neuromediator synthesised in the peripheral and central nerves. CGRP is well represented and molecularly conserved during evolution whereas CT has not been detected in any of the invertebrates analysed so far. In order to better understand the evolution of this CT/CGRP peptide family we reviewed the major data concerning its evolution from the literature and our recent data obtained in models of teleosts and cephalopod molluscs. The presence of both CGRP-like molecules and its specific bindings sites in the central nervous system of eel, cuttlefish and nautilus, suggests that the brain neurotransmitter role of CGRP could represent an ancient role in metazoa, already present in cephalopods and conserved among vertebrates, as still observed in mammals. In contrast, the presence of CGRP specific binding sites, and not the peptide itself, in the gills suggests an endocrine role for CGRP, in cephalopods and teleosts, that may have been lost during the evolution of the tetrapod lineage. These data, and the absence of CT-like molecules that we observed in cephalopods, support the hypothesis that CGRP represents the ancestral molecule of the CT/CGRP family, appeared in metazoa before the vertebrate emergence. The distinction between CT and CGRP receptors appears to be an event posterior to the emergence of ecdysozoan and lophotrochozoan protostomes, probably in relation to the CT appearance. The evolution of the CT/CGRP peptide family is probably similar to the evolution of the CT/CGRP receptor family. In fact, the genic duplication that induced the appearance of the two separate molecules, CT and CGRP, may constitute an event close to that, which induced the appearance of the two specific receptors. These events remain to be further studied in order to better understand the peptide and receptor evolution of the CT/CGRP family.

Endocrinology of protochordates

Large-scale gene duplications occurred early in the vertebrate lineage after the split with protochordates. Thus, protochordate hormones and their receptors, transcription factors, and signaling pathways may be the foundation for the endocrine system in vertebrates. A number of hormones have been identified including cionin, a likely ancestor of cholecytokinin (CCK) and gastrin. Both insulin and insulin-like growth hormone (IGF) have been identified in separate cDNAs in a tunicate, whereas only a single insulin-like peptide was found in amphioxus. In tunicates, nine distinct forms of gonadotropin-releasing hormone (GnRH) are shown to induce gamete release, even though a pituitary gland and sex steroids are lacking. In both tunicates and amphioxus, there is evidence of some components of a thyroid system, but the lack of a sequenced genome for amphioxus has slowed progress in the structural identification of its hormones. Immunocytochemistry has been used to tentatively identify a number of hormones in protochordates, but structural and functional studies are needed. For receptors, protochordates have many vertebrate homologs of nuclear receptors, such as the thyroid, retinoic acid, and retinoid X receptors. Also, tunicates have cell surface receptors including the G-protein-coupled type, such as β-adrenergic, putative endocannabinoid, cionin (CCK-like), and two GnRH receptors. Several tyrosine kinase receptors include two epidermal growth factor (EGF) receptors (tunicates) and an insulin/IGF receptor (amphioxus). Interestingly, neither steroid receptors nor a full complement of enzymes for synthesis of sex steroids are encoded in the Ciona genome. Tunicates appear to have some but not all of the necessary molecules to develop a vertebrate-like pituitary or complete thyroid system.

Calcitropic peptides: neural perspectives

In mammals and higher vertebrates, calcitropic peptides are produced by peripheral endocrine glands: the parathyroid gland (PTH), thyroid or ultimobranchial gland (calcitonin) and the anterior pituitary gland (growth hormone and prolactin). These hormones are, however, also found in the neural tissues of lower vertebrates and invertebrates that lack these endocrine organs, suggesting that neural tissue may be an ancestral site of calcitropic peptide synthesis. Indeed, the demonstration of CNS receptors for these calcitropic peptides and their induction of neurological actions suggest that these hormones arose as neuropeptides. Neural and neuroendocrine roles of some of these calcitropic hormones (calcitonin and parathyroid hormone) and related peptides (calcitonin gene related peptide, stanniocalcin and parathyroid hormone related peptide) are thus the focus of this review.

The presence of immunoreactive vertebrate bioactive peptide substances in hemocytes of the freshwater snail Viviparus ater (Gastropoda, Prosobranchia)

1. Using an immunocytochemical procedure a wide range of immunoreactive vertebrate bioactive peptides (BAPs) has been found in hemocytes of Viviparus ater: bombesin, calcitonin, CCK-8, CCK-39, GH, glucagon, insulin, oxytocin, neurotensin, secretin, serotonin, somatostatin, substance P, vasopressin, and VIP. 2. No immunostaining was observed for antigastrin and antithyroglobulin antibodies. 3. The presence of BAP-like molecules in hemocytes suggests a correlation between hemocyte and APUD cells and is evidence of a relationship between the neuroendocrine and the immune systems.

Pattern of substance P- and cholecystokinin-like immunoreactivity during regeneration of the neural complex in the ascidian Ciona intestinalis

The neural ganglion of ascidians exhibits a novel and rapid pattern of regeneration whereby within approximately 28-35 days of total ablation an entirely new neural complex is formed. In normal adults, neuronal cell bodies expressing substance P- (SP-Li), neurokinin A-(NKA-Li), CCK/gastrin- (CCK-Li), and insulin-like immunoreactivity exhibit a clearly defined pattern of localization in the cortical rind of the ganglion with characteristic long processes arising from the perikarya running throughout the neuropile. CCK-Li cell bodies are particularly concentrated close to the points of exit of the main nerve trunks. We have used antisera raised against these peptides to monitor the process of regeneration up to postoperative (pa) day 35. Only SP and CCK antisera produced positive staining in the regenerating tissue. Immunoreactive cell bodies first appear following 14 days pa. At this time CCK-Li neurons are more abundant than SP-Li neurons and in contrast to the pattern found in the normal adult ganglion, immunoreactive cell bodies are located both peripherally and centrally in the core of the ganglion and processes were rarely seen. Later stages exhibited an increasing number of SP-Li neurons and at 35 days pa SP-Li cell bodies clearly predominate. CCK-Li neurons typically become clustered close to the points of emergence of the anterior nerve roots. The early expression of CCK-Li and SP-Li molecules during regeneration is considered in terms of their potential role in development and cell proliferation in the newly forming ganglion.

Immunocytological localization of endogenous calcitonin-like molecules in the crustacean Orchestia

Immunocytological mapping of calcitonin-like molecules (human form) performed in the terrestrial crustacean Orchestia, using PAP procedure on paraffin sections and immunogold method on ultrathin cryosections, reveals two reactive organs: central nervous system and posterior caeca of the midgut. Immunoreactivity within the nervous system is mainly located throughout perikarya and nerve fibers from both dueto- and tritocerebron and ventral nervous chain. Immunolabeling in the posterior caeca is detected on both cell components of the epithelium, with significant quantitative differences between molt and intermolt periods. The role of calcitonin-like substances in these organs is then discussed: at the nervous system level, a neuro transmitter function is suggested; the direct participation of these peptides in the regulation of calcium shifts through the caecal epithelium is hypothesized.

Cells showing immunoreactivity for calcitonin or calcitonin gene-related peptide (CGRP) in the central nervous system of some invertebrates

In the central nervous system of some species of several invertebrate phyla, including land planarians (Platyhelminthes), ribbon worms (Nemertina), slugs (Mollusca), polychaetes, earthworms and leeches (Annelida), pill bugs (Arthropoda), and beard worms (Pogonophora), salmon calcitonin-immunoreactive cells and rat calcitonin gene-related peptide (CGRP)-immunoreactive cells were found by immunohistochemistry. These immunoreactive cells were located in the region surrounding the neuropile, although the sizes of the cells varied according to species. Some of them were round or polygonal and regarded as apolar nerve cells because of their lack of cytoplasmic processes, whereas others were spindle-shaped or elongated, being comparable with unipolar nerve cells because of extension of their cytoplasmic processes in the direction of the neuropile. In some cases, it was noted that the cytoplasmic processes had complicated branches or formed loop-like structures at their ends. These observations suggest that a calcitonin-like or CGRP-like substance is extensively present in invertebrates as well as vertebrates.

Immunocytochemical evidence of vertebrate bioactive peptide-like molecules in the immuno cell types of the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata)

An immunocytochemical investigation was carried out on round and spreading hemocytes of Planorbarius corneus by using 20 antisera to vertebrate bioactive peptides. The immunotests showed the presence of alpha 1-antichymotrypsin-bombesin-, calcitonin-, CCK-8 (INC)-, CCK-39-, gastrin-, glucagon-, Met-enkephalin-, neurotensin-, oxytocin-, somatostatin-, substance P-, VIP-, and vasopressin-immunoreactive molecules in the spreading hemocytes. The round hemocytes were only positive to anti-bombesin, anticalcitonin, anti-CCK-8 (INC), anti-CCK-39, anti-neurotensin, anti-oxytocin, anti-substance P and anti-vasopressin antibodies. No immunostaining was observed with anti-CCK-8 (Peninsula), anti-insulin, anti-prolactin, anti-thyroglobulin and anti-thyroxin (T4) antibodies. As probably in vertebrates, these bioactive peptides may modulate immuno cell function.

The calcitonin gene peptides: biology and clinical relevance

The calcitonin/CGRP multigene complex encodes a family of peptides: calcitonin, its C-terminal flanking peptide, katacalcin, and a third novel peptide, calcitonin gene-related peptide (CGRP). The 32-amino acid peptide calcitonin inhibits the osteoclast, thereby conserving skeletal mass during periods of potential calcium lack, such as pregnancy, growth, and lactation. This hormonal role is emphasized by observations that lower circulating calcitonin levels are associated with bone loss and that calcitonin replacement prevents further bone loss. Structurally, CGRP resembles calcitonin and has been implicated in neuromodulation and in the physiological regulation of blood flow. Here we review the molecular genetics, structure, and function of the calcitonin-gene peptides as analyzed in the laboratory and focus on more recent clinical studies relating to disorders and therapeutics.

Tachykinins in the central and peripheral nervous system of the ascidian Ciona intestinalis

Immunochemical studies were carried out on the ascidian Ciona intestinalis to determine the character and distribution of the tachykinins neurokinin A (NKA) and substance P (SP). Antisera specific for the C-terminus of mammalian SP, and for the N-terminus of mammalian SP and NKA, were used to monitor tissue extracts from Ciona. Parallel immunocytochemical studies assessed the distribution of these tachykinins in the central and peripheral nervous systems as well as their occurrence in endocrine cells. HPLC and radioimmunoassay established the presence of both C-terminal SP and NKA-like material in extracts from neural ganglion and body wall/pharynx. Immunocytochemistry revealed the C-SP material to be present in a population of small neuronal cell bodies and fibers in the ganglion as well as in cell bodies and fibers in the periphery. The NKA-like material was restricted to separate and larger neuronal perikarya in the ganglion while in the periphery its distribution reflected that of the C-SP-like material. Endocrine cells in the pharyngeal epithelium were reactive only with the C-terminal SP antiserum. N-terminal SP antisera were unreactive both in radioimmunoassay and immunocytochemistry. These findings are in accord with the idea that the tachykinin family is represented by at least two of its members at the prevertebrate stage of evolution. Interestingly, the SP-like material shows strong C-terminal homology with the mammalian peptide but little N-terminal similarity. Furthermore, the NKA-like peptide is restricted to the nervous system while SP-like molecules may be found in both central and peripheral neurons as well as endocrine cells in the pharynx.

Autonomic and sensory innervation of anuran ultimobranchial glands: a horseradish peroxidase study

The extrinsic innervation of the endocrine ultimobranchial glands in the frog were identified by retrograde labeling with horseradish peroxidase. Labeled neurons were seen ipsilateral to the side injected in the caudal region of the vagal motor nucleus, the jugular sensory ganglion and first and second cervical sympathetic ganglia. These studies demonstrate a dual autonomic and vagal sensory innervation of the gland that are compatible with previous ultrastructural studies, but indicate a more complex innervation than previously shown.

Scyliorhinin I and II: two novel tachykinins from dogfish gut

Two peptides with tachykinin-like ability to contract longitudinal muscle from the guinea pig ileum were isolated from the intestine of the common dogfish, Scyliorhinus caniculus. The amino acid sequence of scyliorhinin I was established as Ala-Lys-Phe-Asp-Lys-Phe-Tyr-Gly-Leu-Met-NH2 and this peptide cross-reacted with antisera directed against the C-terminal region fo substance P. The amino acid sequence of scyliorhinin II was established as Ser-Pro-Ser-Asn-Ser-Lys-Cys-Pro-Asp-Gly-Pro-Asp-Cys-Phe-Val-Gly-Leu-Met- NH2 and this peptide cross-reacted with antisera directed against the C-terminal region of neurokinin A. The mammalian peptides substance P and neurokinin A were absent from the dogfish intestinal tissue.

Occurrence and distribution of substance P-related immunoreactivity in the brain of adult lampreys, Petromyzon marinus and Entosphenus tridentatus

The occurrence and distribution of substance P (SP)-related immunoreactivity were examined in the adult brains of two species of lampreys, Petromyzon marinus and Entosphenus tridentatus, by using the PAP technique and three different anti-SP sera (anti-SP#1, anti-SP#2, and anti-SP#3). In both species of lampreys, anti-SP#1 and anti-SP#2 yielded positive reactions in the brain, while there was no, or slight immunoreaction there to anti-SP#3. The positive reactions toward anti-SP sera in the lamprey brain were not eliminated, or insufficiently reduced by preabsorption with SP, but they were completely abolished by preabsorption with eledoisin-related peptide. Thus, SP-positive material in the lamprey brain is more closely related, in terms of immunological determinants, to eledoisin than to SP. In Petromyzon, SP-positive perikarya were found in the ventrolateral telencephalon and the ventral hypothalamus, whereas in Entosphenus they were found in the ventral thalamus, tegmentum motoricum mesencephali (two locations), and rostral rhombencephalon, as well as in the above-mentioned two regions. Nevertheless, the distributions of SP-positive fibers in the regions of the brain other than the neurohypophysis were very similar between the two species: SP-positive fibers were found at many locations of the brain, and were especially rich in the periventricular subependymal zone of the ventral telencephalon and in the diencephalon, preoptic area, hypothalamus, and interpeduncular nucleus. In Petromyzon, a heavy accumulation of positive fibers was observed in the rostral part of the anterior neurohypophysis, whereas in Entosphenus no such fibers were observed there. These results clearly suggest the presence of a neuronal system of unknown function containing a SP-related peptide in the brain of lampreys.

Immunohistochemical and chromatographic studies of peptides with tachykinin-like immunoreactivity in the central nervous system of the lamprey

The distribution and chemical properties of compounds with tachykinin-like immunoreactivity (TK-LI) in the spinal cord and brain of lampreys (Lampetra fluviatilis and Ichthyomyzon unicuspis) were investigated by means of immunohistochemistry and various chromatographic methods combined with radioimmunoassay. The distribution of TK immunoreactive fibers in the lamprey spinal cord was investigated with 13 different TK antisera which gave positive staining in pilot experiments. The antisera were raised against substance P (SP) (n = 6), physalaemin (PHY) (n = 1), neurokinin A (NKA) (n = 2), kassinin (KAS) (n = 2) or eledoisin (ELE) (n = 2). Pre-incubation of these antisera with their corresponding TKs abolished or reduced the immunostaining. Four different patterns of distribution were found with the 13 antisera, and they did not seem to be related to the TKs against which the antisera were raised. The different patterns could be explained by assuming the presence of the three different TKs. Six different antisera, raised against SP (n = 2), KAS (n = 2) or ELE (n = 2), were used for radioimmunoassay. The TK-LI material eluted as several separate components in various chromatographic systems. The central nervous system (CNS) of the lamprey did not contain measurable amounts of SP, NKA, neurokinin B (NKB), KAS or ELE. The present data imply that the lamprey CNS contains at least three different TKs probably different from SP, PHY, NKA, NKB, KAS or ELE; these are possibly new, not earlier described TKs. The three hypothetical TKs differ in their distribution.

Substance P-like immunoreactivity in the central nervous system of the blattarian insect Periplaneta americana L. revealed by a monoclonal antibody

Brains, retrocerebral complexes and frontal and suboesophageal ganglia of adult American cockroaches, Periplaneta americana, were immunohistochemically investigated with a specific monoclonal antibody (McAb) directed against a well characterized antigenic determinant, namely the COOH terminus of the endecapeptide substance P (SP). This resulted in the detection of several neurons and nerve fibres containing a substance antigenically closely related to this typically vertebrate neuropeptide. No difference in staining pattern could be observed between male and female insects. Related to the age of the adult specimens, however, a slight quantitative difference in SP immunoreactivity seems to occur, which probably might have functional implications. The SP-like peptide demonstrated in this study appears to be located in different neuronal structures than the ones that we earlier described as containing ACTH-, CRF-, OT-, AVP-, NP I-, NP II-, BPP-, FMRFamide-, AKH-, met-ENK-, FSH-, LH- and LHRF-like material (Verhaert et al. 1984a, b, 1985; Verhaert and De Loof 1985a, b).

Novel peptides from the calcitonin gene: expression, receptors and biological function

Calcitonin gene products include calcitonin and its carboxyl-terminal flanking peptide (in man PDN-21), and calcitonin gene-related peptide (CGRP). Alternative splicing of the initial gene transcripts results in the production of two distinct messenger RNA encoding precursors of CGRP and of calcitonin. CGRP messenger RNA is the predominant transcription product of the calcitonin gene in neural tissues, but it is also present in the pituitary and the C-cells of normal thyroid glands and in medullary thyroid carcinoma. Immunoreactive CGRP has, moreover, been recognized around blood vessels of the heart. Calcitonin and PDN-21 are cosecreted from thyroid C-cells, but they are also found in the brain and pituitary. CGRP receptors are present in the brain and the heart, and calcitonin receptors in bone and kidney cells and in the hypothalamus. Calcitonin administered peripherally and in vitro inhibits bone resorption and stimulates renal 1.25-dihydroxycholecalciferol production. CGRP used in the same manner has potent cardiovascular effects (vasodilation, hypotension, positive chronotropic and inotropic action in the heart). Intracerebroventricular administration of CGRP raises the blood pressure, and both CGRP and calcitonin inhibit gastric acid secretion and food intake. The distinct but overlapping effects of calcitonin and CGRP raise important regulatory and functional issues.

CCK-like peptides in the neural complex of a protochordate

The neural complex of the ascidian Styela plicata has been investigated by means of cytochemical and immunocytochemical methods. In the cerebral ganglion, using a mammalian antibody to synthetic CCK-8, immunoreactive neurons and nerve fibers have been localized; at the same time immunofluorescent cells are scattered in some glandular lobules of the neural gland. The possible functions of a CCK-8-like peptide in ascidians is suggested and discussed.

Immunohistochemical distribution of somatostatin-like immunoreactivity in the central nervous system of the adult rat

The localization and distribution of somatostatin (growth hormone release-inhibiting hormone; somatotropin release-inhibiting factor) have been studied with the indirect immunofluorescence technique of Coons and collaborators and the immunoperoxidase method of Sternberger and coworkers using specific and well-characterized antibodies to somatostatin, providing semiquantitative, detailed maps of somatostatin-immunoreactive cell profiles and fibers. Our results demonstrate a widespread occurrence of somatostatin-positive nerve cell bodies and fibers throughout the central nervous system of adult, normal or colchicine-treated, albino rats. The somatostatin cell bodies varied in size from below 10 micron up to 40 micron in diameter and could have only a few or multiple processes. Dense populations of cell somata were present in many major areas including neocortex, piriform cortex, hippocampus, amygdaloid complex, nucleus caudatus, nucleus accumbens, anterior periventricular hypothalamic area, ventromedial hypothalamic nucleus, nucleus arcuatus, medial to and within the lateral lemniscus, pontine reticular nuclei, nucleus cochlearis dorsalis and immediately dorsal to the nucleus tractus solitarii. Extensive networks of nerve fibers of varying densities were also found in most areas and nuclei of the central nervous system. Both varicose fibers as well as dot- or "dust-like" structures were seen. Areas with dense or very dense networks included nucleus accumbens, nucleus caudatus, nucleus amygdaloideus centralis, most parts of the hypothalamus, nucleus parabrachialis, nucleus tractus solitarii, nucleus ambiguus, nucleus tractus spinalis nervi trigemini and the dorsal horn of the spinal cord. One exception is the cerebellum which only contained few somatostatin-positive cell bodies and nerve fibers. It should be noted that somatostatin-positive cell bodies and fibers did not always conform to the boundaries of the classical neuroanatomical nuclei, but could often be found in areas between these well-established nuclei or occupying, in varying concentrations, only parts of such nuclei. It was difficult to identify with certainty somatostatin-immunoreactive axons in the animals studied. Some pathways could, however, be demonstrated, but further experimental studies are necessary to elucidate the exact projections of the somatostatin-immunoreactive neurons in the rat central nervous system.

Methionine-enkephalin-like immunoreactivity in the nervous ganglion and the ovary of a protochordate, Ciona intestinalis

When methionine-enkephalin antiserum was applied to paraffin sections of adult Ciona intestinalis it reacted with neurons in the ganglion and along the visceral nerve. The fluorescence was strong before and during spawning season, but partially disappeared at the end of August. With the same antibody a positive immunoreactivity was detected in the ovary during the growth of oocytes. The distribution of positive granules in the cytoplasm did not change significantly with varying lighting conditions (normal photoperiod, permanent light or darkness) in which the animals were maintained. In contrast, treatment with a substance isolated from crude extracts of Ciona ("peroxide 1") induced a dense, crescent-like concentration of positive granules near the nucleus of oocytes. The follicular cells did not show any immunofluorescent reaction.

Prolactinergic neurons in a protochordate

Peptidergic neurons have been detected in the cerebral ganglion of the ascidian Styela plicata by means of cytochemical methods. After incubation with a mammalian antibody to human prolactin the perikarya show a strong immunoreactivity. The possible function of prolactin-like peptides in the nervous system of protochordates is discussed.

Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing

Alternative processing of the RNA transcribed from the calcitonin gene appears to result in the production of a messenger RNA in neural tissue distinct from that in thyroidal 'C' cells. The thyroid mRNA encodes a precursor to the hormone calcitonin whereas that in neural tissues generates a novel neuropeptide, referred to as calcitonin gene-related peptide (CGRP). The distribution of CGRP-producing cells and pathways in the brain and other tissues suggests functions for the peptide in nociception, ingestive behaviour and modulation of the autonomic and endocrine systems. The approach described here permits the application of recombinant DNA technology to analyses of complex neurobiological systems in the absence of prior structural or biological information.

Immunohistochemical demonstration of peptides, serotonin and dopamine-beta-hydroxylase-like material in the nervous system of the leech Hirudo medicinalis

The central ganglia of the leech, Hirudo medicinalis, were processed for the immunohistochemical localisation of bombesin-, substance P-, cholecystokinin-, vasoactive intestinal polypeptide-, enkephalin-, serotonin- and dopamine-beta-hydroxylase-related substances. To varying extents all of the substances were localised in neuropile processes, and all, with the exception of substance P, were associated with specific perikarya. The most prominent neuropeptides, in terms of the number of immunoreactive neurones, were cholecystokinin and vasoactive intestinal peptide. The dopamine-beta-hydroxylase positive neurones are thought to be octopaminergic, and the serotonin monoclonal antibody revealed positive staining in the Retzius cells. We were unable to demonstrate the coexistence of pairs of substances in any neurones in the leech ganglia.

Cholecystokinin (CCK)/gastrin-like immunoreactive neurones in the cerebral ganglion of the protochordate ascidians Styela clava and Ascidiella aspersa

Antisera raised against the COOH-terminal sequence of mammalian CCK/gastrin were used to ascertain the distribution of CCK/gastrin-like immunoreactive cells in the cerebral ganglion of two ascidian protochordates. Styela clava and Ascidiella aspersa. the cell bodies were found to have a specific regional distribution in Ascidiella, but not in Styela. In addition to central immunoreactive nerve fibres, a number of peripherally located immunoreactive fibres was found. These observations support the idea that some centrally originating protochordate neuronal peptides may have a peripheral role and give weight to the hypothesis that many vertebrate brain-gut peptides had their origin in the neuronal elements of more primitive species.

Gastro-intestinal and neurohormonal peptides in the alimentary tract and cerebral complex of Ciona intestinalis (Ascidiaceae)

Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion of Ciona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods. Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP), beta-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP). Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for beta-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract. No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion. At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.

Calcitonin: regional distribution of the hormone and its binding sites in the human brain and pituitary

Immunoreactive calcitonin (CT), indistinguishable from human CT-(1-32) and its sulfoxide, has been identified in extracts of the hypothalamus, the pituitary, and the thyroid obtained from human subjects at autopsy. DCT concentrations were highest in a region encompassing the posterior hypothalamus, the median eminence, and the pituitary; intermediate in the substantia nigra, the anterior hypothalamus, the globus pallidus, and the inferior colliculus; and low in the caudate nucleus, the hippocampus, the amygdala, and the cerebral and cerebellar cortices. Specific CT binding measured with 125I-labeled salmon CT was highest in homogenates of the posterior hypothalamus and the median eminence, shown to contain the highest concentrations of endogenous CT in the brain; CT binding was less than 12% of hypothalamic binding in all of the other regions of the brain examined and was negligible in the pituitary. Half-maximal binding was achieved with 0.1 nM nonradioactive salmon CT-(1-32), and the binding was directed to structural or conformational sites, or both, in the COOH-terminal half of salmon CT. The rank order of the inhibition of the binding by CT from different species and analogues of the human hormone was the same as in receptors on a human lymphoid cell line (Moran, J., Hunziker, W. & Fischer, J. A. (1978) Proc. Natl. Acad. Sci. USA 75, 3984-3988). The functional role of CT and of its binding sites in the brain remains to be elucidated.